Baruch Shem Kivod Malchuto V: Aruch HaShulchan
All our hopes and aspirations are for God to reveal His Unity to the entire Creation, when all will see and acknowledge God as King of the Universe. Baruch Sheim is the expression all the inhabitants of the world will use at that time.
We immediately respond Baruch Shem after declaring God’s unity, Hashem Echad – we join in the words all will say when they understand that Hashem Echad. We whisper the words because it has yet to happen. (Aruch Hashulchan O”C 74)